You can add calling credits in the event that you exceed your plan minutes with the Auto Purchase feature.

This feature ensures your RingCentral account to never run out of calling credits. When you select a package, it will be purchased automatically when you start running low on calling credits which would definitely prevent any hassle or interruption with your service.

To view further instructions on the Auto-Purchase feature, like how to set it up, click this link: Article Number: 5247.